The present invention relates to sealing members for butterfly valves, and more specifically to removable and replaceable valve sealing members.
Butterfly valves are well known wherein a valve body, which is generally a cylindrical member for allowing fluid to flow therethrough, has a valve seat formed therein and a movable valve disc is carried on a rotatable shaft such that the valve disc can be moved into and away from sealing engagement with the valve body seat. Thus, in such a valve there are two sealing surfaces, one sealing surface is the valve seat in the valve body, while the other sealing surface is carried on a periphery of the valve disc. When the disc is brought into contact with the seat, a seal is formed.
In one type of butterfly valve presently available, the valve seat is formed integrally with the valve body and the sealing member on the valve disc is replaceable and is held onto the valve disc by a retainer ring held in place by cap screws.
In another type of butterfly valve presently available, the valve disc comprises a single unitary member and a removable and replaceable seal member is mounted to the valve body by means of a retaining ring held in place in the valve body by cap screws. In this type of arrangement the cross sectional flow area through the valve body is reduced in order to provide sufficient area for the cap screws to engage into the valve body and for the retaining ring to hold the ring-like seal member in place.
Butterfly valves can be used in a wide variety of installations within a pipeline, wherein the pipeline may carry a wide range of different fluids. In some instances the fluids may be corrosive or may have a relatively high temperature or relatively low temperature, and even might carry some solids. In the operation of a butterfly valve, due to the fluid and material flowing through the valve body when the disc is in an open position, sometimes the sealing surfaces carried by the disc or within the valve body becomes cut, scratched or damaged in some other fashion. When this occurs it is necessary to repair the sealing surfaces in order to be assured that complete sealing will be provided. However, in present constructions it is possible to only replace one of the two sealing surfaces, thus preventing complete repairability of the butterfly valve when both surfaces are damaged.
In order to provide enhanced sealing and reduced wear between the movable disc and the valve body seat, special geometries and constructions are used. For example, in some constructions the valve disc is carried on a shaft and the shaft rotates to move the disc relative to the valve body seat, however, the shaft is offset longitudinally (relative to the fluid flow centerline of the valve body) from the sealing area between the disc and the valve body seat. Thus, an axis of rotation of the disc shaft is parallel to, but offset from, a plane in which the valve disc engages the valve body seat.
A second offset may be provided for the valve disc shaft. This second offset is a lateral offset such that although the axis of rotation of the valve shaft is perpendicular to the flow through centerline of the valve body, the valve disc shaft is laterally offset so that its axis of rotation does not intersect the centerline of the valve body.
Third, it has been found that by making the valve seat have a frusto-conical shape and having the valve disc have a complementary frusto-conical shape enhances the sealing characteristics of the butterfly valve. A third offset is to incline the angle of the frusto-conical shapes such that if the shape was projected out to an apex, the apex would be offset from the centerline of the valve body.
The valve bodies are connected at each end to a pipe forming a pipeline, and the connection can be one of a variety of different connection types. For example, the pipe ends may be flanged and the valve body also flanged with a series of apertures therethrough for receiving mounting bolts to secure the valve body within the pipeline. Alternatively, instead of a full flange, a series of angularly spaced lugs may be provided around the periphery of each end of the valve body to align with similar lugs or a flange on the pipe for receiving securing bolts. Also, the valve body may be a wafer style which is relatively thin and which is positioned between flanges in the pipe and is clamped between the flanges. Further, the valve body may be arranged to be welded to the pipe or even threaded to the pipe.